1. Field of the Invention
This invention relates broadly to telecommunications. More particularly, this invention relates to methods and apparatus for controlling the flow of multiple SONET signal streams over a single full duplex ETHERNET link.
2. State of the Art
The TRANSWITCH ETHERMAP-12 is a highly integrated OC-12 mapper for carrying ETHERNET traffic over SONET/SDH networks utilizing Virtual Concatenation (VCAT). It supports STM-4/STS-12/STS-12c rates using a parallel telecom bus operating at 77.76 MHz. The device supports up to eight 10 Mbps or 100 Mbps ETHERNET ports using the SMII interface standard or a single Gigabit (1,000 Mbps) ETHERNET port using the GMII interface standard.
When the ETHERMAP-12 is operated in the SMII mode, eight FIFOs are provided, one for each ETHERNET port, each ETHERNET port being associated with one SONET port, virtual port or virtual concatenated group (VCG). Each FIFO has a high and a low threshold point which are associated with defined Xon (transmit data on) and Xoff (transmit data off) conditions. When a FIFO exceeds the Xoff threshold, a pause frame is generated. The pause duration is programmable and is identified in the pause frame. When the FIFO re-crosses the Xon threshold, a pause frame with a very short pause duration is generated. When operated in the SMII mode, the ETHERMAP-12 can support an OC-3 ring (155 Mbps) by combining two of the eight ETHERNET ports.
When the ETHERMAP-12 is operated in Gigabit mode, a single FIFO is provided for the single Gigabit ETHERNET port. In this mode, the ETHERMAP-12 supports a single OC-12 ring (622 Mbps). It would be desirable to multiplex a plurality of SONET ports, virtual ports or virtual concatenated groups (VCGs) over the single Gigabit ETHERNET link. For example, it would be desirable to support multiple OC-3 rings in the Gigabit mode of the ETHERMAP-12.